1. Field of the Invention
The present invention relates to an ink jet recording apparatus that performs recording by discharging ink from recording means to a recording medium.
2. Related Background Art
Conventionally, the recording apparatus that records on a recording medium, such as paper, cloth, plastic sheet, or OHP sheet, among some other materials (hereinafter, also, simply referred to as a “recording sheet”) has been proposed in a mode in which a recording head of wire-dot method, thermal sensitive method, thermal transfer method, ink jet method, or the like is made mountable thereon, for example.
Of such recording apparatuses, the one that adopts an ink jet recording method for recording on a recording sheet by discharging ink from the ink discharge ports (hereinafter, referred to as an ink jet recording apparatus) is of non-impact type, which produces a lesser amount of noise, and makes it possible to perform a recording operation in high density at high speed. Generally, the ink jet recording apparatus is provided with means for driving a carriage having the recording head mounted thereon; conveying means for conveying a recording sheet; and control means for controlling them.
Meanwhile, as the energy-generating element that generates energy to be utilized for discharging ink from the ink discharge ports of a recording head, there is the one that uses an electro-mechanical converting element, such as a piezo-element, the one that generates heat by irradiating electromagnetic waves to thereby discharge ink droplets, such as a laser, or the one that heats liquid by use of an electrothermal converting element provided with a heat-generating resistor member, among some others.
Of the recording heads of such kinds, the recording head of the ink jet recording method that discharges ink as liquid droplets by the utilization of thermal energy makes it possible to perform recording in high resolution, because the ink discharge ports can be arranged in high density. Among them, the recording head that uses electrothermal converting elements as energy-generating elements has such advantage as to realize miniaturization with ease, which can be manufactured and assembled in high density at lower manufacturing costs by the full utilization of the advantages of the IC technologies and techniques, and micro-processing art having made remarkable technical advancement and the enhancement of reliability in the semiconductor field in recent years.
As described above, the ink jet recording method makes an extremely excellent recording performance possible with a simple structural arrangement. On the other hand, however, there also exist problems yet to be solved.
As the problems of the ink jet recording method, the scratches or unprinted lines of recorded images and the increased density of ink may be encountered due to the evaporation of ink from discharge ports, or the various ink colors may intermix in the discharge ports after the execution of the suction recovery operation, among some other causes. In order to solve these problems, it is generally practiced to perform the so-called preparatory discharges, which are the discharges not related to the image formation. More specifically, the predetermined preparatory discharges are effectuated in the preparatory ports or in a cap, based on the time that has elapsed since the last performance of the preparatory discharge or based on the time that has elapsed since the previous capping. Then, it is known that the number of preparatory discharges is made different in accordance with the time that has elapsed since the last preparatory discharge or the time that has elapsed since the last capping.
Also, in the specification of U.S. Pat. No. 5,701,146, there is the disclosure as to an art whereby to suck and exhaust ink in the cap under the atmosphere, while executing preparatory discharges in the cap, in order to enhance the recovery capability of a recording head or the surface of a recording head.
However, it is known that when preliminary discharges are performed, there tends to occur the phenomenon that there are floating in the apparatus the fine ink droplets that accompany ink droplets discharged or the fine ink droplets generated by part of rebounded ink droplets which are landed onto the cap, or, further, the discharged ink droplets themselves, which makes flying speed slower before the droplets are impacted, due to the influence of air resistance or the like. The ink droplets and others that float in the apparatus are collectively called “mist”, and if there is the floating of a considerable amount of mist, the adhesion thereof occurs on the components in the apparatus, leading to various kinds of drawbacks eventually. If a considerable amount of mist adheres to the parts, which are in contact with a recording medium, the recording medium is stained, and if the surface thereof is stained, it results even in the degradation of recording quality. Also, if a considerable amount of mist adheres to the parts, such as an optical sensor, it becomes impossible to carry out exact detection, leading to the operational drawback, and the degradation of recording quality may ensue or the recording apparatus is caused to be out of order in some cases. Also, if a considerable amount of mist adheres to the parts that the user may handle, his hand may be stained unavoidably.
Here, it is known that in order to suppress the mist generation of such kind, preliminary discharges are performed in the status of having the cap capped to the discharge port surface of the recording head, which cap is usually used for the prevention of ink evaporation from the discharge ports. Nevertheless, although it becomes possible to suppress the mist generation by the performance of preliminary discharges in the status where the discharge port surface is capped, there is a problem that the time of recording on a recording medium takes more time, because it requires a time to execute the capping operation to enable the cap to be in contact with the discharge port surface.